The present invention relates to a mold closing unit especially for a hot chamber die-casting machine having a machine stand and a guide surface located thereon for the closing unit operable by a crosshead. A vertical adjustment device in the form of a shear mechanism supports the closing unit, is located below the latter, and rests on the guide surface. The shear mechanism is capable of being spread apart by a drive assembly.
A mold closing unit of this type is known from DE 30 18 288 C2. Such a design has the advantage that the vertical adjustment device for the mold closing unit can be made very simple. Several lifting cylinders that must be controlled simultaneously and in the same direction are superfluous.
In the known design, a hydraulic piston is provided as the drive assembly for spreading the shear mechanism apart. The piston is guided in a pressure cylinder located directly in the crosshead. This design, which has an advantage in that no extra space is required in the machine stand for containing a pressure cylinder, makes it necessary to design and operate the crosshead in a special fashion.
It is an object of the present invention to provide a simple design for a mold closing unit of the type mentioned above.
To achieve this object, provision is made, in a mold closing unit of the type mentioned above, for a drive assembly formed by an electric servomotor located below the guide surface and aligned with its axis perpendicular to a drive direction. The servomotor operates a spindle drive engaging the shear mechanism through an angle transmission.
As a result of this design, a pressure cylinder arrangement in the crosshead is unnecessary. The space requirement for providing the servomotor below the guide surface is small because the servomotor has a length which is essentially parallel to the guide surface. It has been found that, when corresponding transmission ratios are used in this manner, relatively high supporting forces for the closing unit can be readily applied by electric motors, and a much finer tuning of the lifting speeds can be achieved in this manner without the construction cost becoming too great.
According to one feature of the invention, the servomotor can be designed as a geared brake motor so that, even if the power fails, there is no danger that the closing unit will fall back from its position once its position is set.
It is advantageous to have the axis of the servomotor aligned parallel with guide rods of the closing unit because then the space requirement for locating the motor can be minimized. According to a particularly advantageous feature of the invention, one end of one lever of the shear mechanism can be mounted pivotably on a housing part of the angular transmission, firmly mounted in the machine stand, while one end of another lever of the shear mechanism, not mounted on the angular transmission, can be located pivotably in a pressure element in the closing unit.
An embodiment of the invention is shown in the drawings and will be described below.